The present invention relates to bio-oxidation and nitrification modules useful in the treatment of sewage and industrial wastewater and pertains more particularly to apparatus and a process for manufacturing such modules.
The bio-oxidation and nitrification of sewage and industrial wastewater normally is carried out in towers that are "packed" with treatment modules that provide a large surface area upon which micro-organisms can grow. For a number of years, such treatment towers usually were filled with rocks having an average diameter of about 5 to 10 centimeters over which the sewage or industrial wastewater was "trickled". The aerobic bacterial growth that formed on the surface of the rocks converted organic material and inorganic nutrients in the wastewater into relatively stable products (such as biological solids, carbon dioxide, nitrates and nitrites). The solid materials are removed from the treated wastewater before the wastewater is treated further or returned to the environment.
In more recent times, the rock packing in the treatment towers has been replaced with treatment media in the form of modules comprised of alternating flat and corrugated sheets. The sheets usually are made of rigid plastic material, such as polyvinyl chloride, polyethylene, polypropylene or polystyrene. A typical module is about 60 centimeters wide, about 120 centimeters long, and about 60 centimeters high. A number of modules are stacked on top of each other within the tower, the stacked modules often reaching a height of 10 to 15 meters. The thickness of the sheets and their rigidity must be sufficient to withstand collapse during normal use of the treatment tower. The corrugations of the corrugated sheets usually extend across essentially the entire dimension of the sheet and preferably are sinuous to avoid straight "fall-through" of the wastewater through the module.
In the fabrication of such modules, "solvent bonding" has been used extensively to produce a strong bond between adjacent flat and corrugated sheets of the module. To achieve the bond, a volatile solvent for the plastic from which the sheets are formed is applied to the interfacing surfaces of the sheets, the solvent softening the interfacing surfaces of the sheets. The assembly of alternating flat and corrugated sheets is placed under a slight pressure so that the softened interfacing surfaces are held in contact with each other until the solvent evaporates from the surfaces. Fusion of the contacting interfacing surfaces occurs upon the evaporation of the solvent from the plastic. Many of the solvents which are useful for solvent bonding, however, are believed to be hazardous to the health of persons who are exposed over prolonged periods of time to the solvent. As a consequence, it has been suggested that alternate methods of forming the modules be sought.